1. Field of the Invention
The present invention in general relates to a radio circuit in which the frequency of a local oscillator differs from the transmit frequency or the receive frequency and to a mobile radio apparatus using the same.
2. Related Art of the Invention
In recent years, the mobile communication has rapidly become pervasive and for the radio circuit, it is important to achieve smaller size and lower power consumption. Hereinafter, an example of a conventional radio circuit will be described with reference to the drawing.
FIG. 5 shows the construction of the conventional radio circuit. In FIG. 5, reference numeral 41 represents a first local oscillator, reference numeral 42 represents a second transmit local oscillator, reference numeral 43 represents a second receive local oscillator, reference numeral 44 represents a receive frequency converter, reference numeral 45 represents a demodulator, reference numeral 46 represents a transmit frequency converter, reference numeral 47 represents a modulator, reference numeral 48 represents a receive amplifier, reference numeral 49 represents a transmit amplifier, reference numeral 50 represents a duplexer, and reference numeral 51 represents an antenna.
The modulator 47 modulates the output signal of the second transmit local oscillator 42 with a modulating signal to output a transmit intermediate frequency signal. The transmit intermediate frequency signal is converted into a transmit frequency by the first local oscillator 41 at the transmit frequency converter 46, amplified by the transmit amplifier 49, passed through the duplexer 50 and sent out from the antenna 51. The receive signal received by the antenna 51 is passed through the duplexer 50 and amplified by the receive amplifier 48. The amplified receive signal is input to the receive frequency converter 44 to be frequency-converted into a receive intermediate frequency signal with the output of the first local oscillator 41. The demodulator 45 demodulates the receive intermediate frequency signal into a baseband signal with the output of the second receive local oscillator 43.
However, with this arrangement, three local oscillators 41, 42 and 43 are required and it is therefore difficult to achieve size reduction. In addition, since the local oscillators generate different frequencies, spurious emission readily occurs in transmitting signals and interference readily arises in receiving signals.
In view of the above-mentioned problems of the conventional radio circuit, it is an object of the present invention to provide a radio circuit suitable for size reduction and in which undesired spurious emission does not occur.
A radio circuit of the present invention comprises a local oscillator, a first receive frequency converter, a frequency divider and a demodulator,
wherein a receive signal and an output of the local oscillator are input to the first receive frequency converter, the receive signal is converted into a signal of a first intermediate frequency by the first receive frequency converter, the signal of the first intermediate frequency is input to the demodulator, the output of the local oscillator is frequency-divided by the frequency divider and input to the demodulator, the signal converted into the first intermediate frequency is demodulated into a baseband signal by the demodulator.
A radio circuit of the present invention comprises a local oscillator, a first receive frequency converter, a second receive frequency converter, a frequency divider and a demodulator,
wherein a receive signal and an output of the local oscillator are input to the first receive frequency converter, the receive signal is converted into a signal of a first intermediate frequency by the first receive frequency converter, the signal of the first intermediate frequency is input to the second receive frequency converter, the output of the local oscillator is frequency-divided by the frequency divider and input to the second receive frequency converter, the signal of the first intermediate frequency is frequency-converted into a signal of a second intermediate frequency by the second receive frequency converter, the signal converted into the second intermediate frequency and a reference signal of the local oscillator are input to the demodulator, the signal of the second intermediate frequency is demodulated into a baseband signal by the demodulator, and a frequency of the reference signal equals the second intermediate frequency.
A radio circuit of the present invention comprises a local oscillator, a transmit frequency converter, a frequency divider and a modulator, wherein an output of the local oscillator is input to the transmit frequency converter and is also input to the frequency divider to be frequency-divided, an output signal of the frequency divider is input to the modulator, the output signal of the frequency divider is modulated into a transmit intermediate frequency signal by the modulator with a modulating signal, and the transmit intermediate frequency signal is input to the transmit frequency converter to be frequency-converted into a signal of a transmit frequency.
A radio circuit of the present invention comprises a local oscillator, a frequency divider, a modulator and a local frequency converter, wherein an output of the local oscillator is input to the frequency divider to be frequency-divided, the local frequency converter. receives the output of the local oscillator and an output of the frequency divider to output a signal of a transmit frequency, and the modulator modulates an output of the local frequency converter with a modulating signal to output a signal of the transmit frequency.